Lubricating oil composition for internal combustion engine

ABSTRACT

Provided is a lubricating oil composition for internal combustion engine, which further reduces the friction to exhibit excellent fuel efficiency performance. A lubricating oil composition for internal combustion engine, which contains (A) a lubricant base oil having a dynamic viscosity of 2.0 to mm 2 /s at 100° C., (B) a molybdenum-based friction modifier in an amount of 0.005 to 0.2% by mass, in terms of a molybdenum content, based on the mass of the composition, (C) a salicylate-based metal detergent in an amount of 0.01 to 1% by mass, in terms of a metal content, based on the mass of the composition, and (D) at least one compound selected from amino acids having an alkyl group, alkenyl group, or acyl group having 15 to 24 carbon atoms and/or derivatives thereof in an amount of 0.01 to 10% by mass.

TECHNICAL FIELD

The present invention relates to a lubricating oil composition for internal combustion engine, which has improved fuel efficiency.

BACKGROUND ART

Since the oil crisis, automobiles have been improved in fuel efficiency, and, from the viewpoint of protecting the resources and the environment, the improvement of fuel efficiency is still one of the important tasks for automobiles, and is increasingly needed recently. The improvement of the fuel efficiency of automobiles has been made by reducing the car body weight, improving the combustion of the engine, and reducing the friction of the engine or driving system. A method for reducing the friction of the engine includes an improvement of the valve system mechanism, a reduction of surface roughness of the sliding member, and the use of a lubricating oil composition for internal combustion engine (engine oil) having an improved fuel efficiency.

Among these methods, the use of an engine oil having an improved fuel efficiency is excellent in view of the cost, and therefore is becoming common to the market. With respect to the improvement of the fuel efficiency by an engine oil, studies have been made on the reduction of viscosity of the engine oil intended to reduce the friction loss of a piston system, hearing portion, and the like under fluid lubrication conditions. Further, the addition of a friction reducing agent, such as an organomolybdenum compound, to the engine oil intended to reduce the friction loss of a valve system and the like under mixed lubrication and boundary lubrication has been proposed.

With respect to the above-mentioned fuel-efficient engine oil, for example, PTL 1 has proposed an engine oil composition containing a specific additive (such as an alkaline earth metal salicylate detergent or a molybdenum dithiocarbamate friction reducing agent) in a specific amount in a base oil having a dynamic viscosity of 2 to 8 mm²/s at 100° C. and having an aromatic content of 15% by mass. PTL 2 has proposed a lubricating oil composition for internal combustion engine, which has a molybdenum-based friction modifier or an ester or amine ash-free friction modifier and overbased Ca salicylate incorporated into a lubricant base oil containing an ester lubricant base oil having a dynamic viscosity of 3 to 8 mm²/s at 100° C. Further, PTL 3 has proposed a lubricating oil composition for internal combustion engine, which has incorporated a combination of molybdenum oxysulfide dithiocarbamate, an acid amide compound, and an ash-free friction modifier, such as an aliphatic partial ester compound and/or an aliphatic amine compound.

However, the molybdenum-based friction modifier has problems in that it has a limitation of the friction reducing effect even when the amount of the molybdenum-based friction modifier incorporated is increased, and in that the molybdenum-based friction modifier forms precipitate in the oil to cause the oil to be unstable. Further, even when using the molybdenum-based friction modifier and an ester-based or amine-based ash-free friction modifier in combination, almost no further improvement of the friction reducing effect has been recognized. In addition, recently, the lubricating oil is required to have much higher fuel efficiency, and conventional engine oils have not yet achieved satisfactory fuel efficiency.

Meanwhile, sarcosine and aspartic acid derivatives are known as an ash-free friction modifier (for example, PTL's 4 to 6). However, not only the incorporation of such an ash-free friction modifier into a lubricating oil composition for internal combustion engine but also a synergy in the reduction of friction obtained from the ash-free friction modifier and a molybdenum-based friction modifier used in combination have not been known, and those skilled in the art have not been able to expect such an effect.

CITATION LIST Patent Literature

PTL 1: JP-A-8-302378

PTL 2: JP-A-2005-41998

PTL 3: JP-A-2008-106199

PTL 4: JP-A-9-316475

PTL 5: JP-A-2008-179669

PTL 6: JP-A-2005-290181

SUMMARY OF INVENTION Technical Problem

The present invention solves the above-mentioned problems, and a task to be achieved by the invention is to provide a lubricating oil composition for internal combustion engine, which further reduces the friction to exhibit excellent fuel efficiency performance.

Solution to Problem

The present inventor has conducted extensive and intensive studies with view toward solving the above-mentioned problems. As a result, it has been found that further reduction of the friction and fuel efficiency performance can be achieved by a lubricating oil composition for internal combustion engine, which contains (A) a lubricant base oil having a dynamic viscosity of 2.0 to 5.0 mm²/s at 100° C., (B) molybdenum-based friction modifier, (C) a salicylate-based metal detergent, and (D) at least one compound selected from amino acids having an alkyl group, alkenyl group, or acyl group having 15 to 24 carbon atoms and/or derivatives thereof in their respective predetermined amounts.

The present invention has been made based on the above findings, and is as follows.

[1] A lubricating oil composition for internal combustion engine, which contains (A) a lubricant base oil having a dynamic viscosity of 2 0 to 5.0 mm²/s at 100° C., (B) a molybdenum-based friction modifier in an amount of 0.005 to 0.2% by mass, in terms of a molybdenum content, based on the mass of the composition, (C) a salicylate-based metal detergent in an amount of 0.01 to 1% by mass, in terms of a metal content, based on the mass of the composition, and (D) at least one compound selected from amino acids having an alkyl group, alkenyl group, or acyl group having 15 to 24 carbon atoms and/or derivatives thereof in an amount of 0.01 to 10% by mass.

[2] The lubricating, oil composition for internal combustion engine according to item [1] above, wherein the salicylate-based metal detergent (C) is a salicylate-based metal detergent containing boron.

[3] The lubricating oil composition for internal combustion engine according to item [1] or [2] above, which has an HTHS viscosity of 1.9 to 2.7 mPa/s at 150° C.

[4] The lubricating oil composition for internal combustion engine according to any one of items [1] to [3] above, which has an HTHS viscosity of 1.9 to 2.4 mPa/s at 150° C.

[5] The lubricating oil composition for internal combustion engine according to any one of items [1] to [4] above, which has a NOACK evaporation amount of 15% by mass or less.

[6] The lubricating oil composition for internal combustion engine according to any one of items [1] to [5] above, which contains (E) a zinc dialkyldithiophosphate anti-wear agent in an amount of 0.02 to 0.20% by mass, in terms of a phosphorus content, based on the mass of the composition.

Advantageous Effects of Invention

The lubricating oil composition for internal combustion engine of the present invention exhibits remarkable effects such that it has a low coefficient of friction and excellent fuel efficiency performance.

DESCRIPTION OF EMBODIMENTS (A) Lubricant Base Oil

With respect to the lubricant base oil in the invention, there is no particular limitation as long as it is a lubricant base oil having a dynamic viscosity of 2.0 to 5.0 mm²/s at 100° C., and there can be used any of a mineral oil and a synthetic oil which are used as a lubricant base oil in a general lubricating oil composition for internal combustion engine.

The dynamic viscosity at 100° C. of the lubricant base oil is 2.5 mm²/s or more, more preferably 3.0 mm²/s or more, further preferably 3.5 mm²/s or more, especially preferably 3.8 mm²/s or more, most preferably 4.0 mm²/s or more, and is preferably 4.5 mm²/s or less, further preferably 4.3 mm²/s or less.

When the dynamic viscosity at 100° C. of the lubricant base oil is less than 2.0 mm²/s, the oil film formation at the lubricating site is unsatisfactory so that the lubricating properties become poor, and further an evaporation loss of the lubricant base oil is increased. On the other hand, when the dynamic viscosity at 100° C. of the lubricant base oil is more than 5.0 mm²/s, the fuel efficiency effect is reduced, and further the low-temperature viscosity properties become poor.

In the invention, the dynamic viscosity at. 100° C. indicates a dynamic viscosity at 100° C. defined in ASTM D-445.

The dynamic viscosity at 40° C. of the lubricant base oil in the invention is preferably 14 mm²/s or more, more preferably 16 mm²/s or more, further preferably 18 mm²/s or more, and is preferably 25 mm²/s or less, more preferably 23 mm²/s or less, more preferably 22 mm²/s or less, further preferably 21 mm²/s or less, especially preferably 20 mm²/s or less. The dynamic viscosity at 40° C. in the invention indicates a dynamic viscosity at 40° C. defined in ASTM D-445. When the dynamic viscosity at 40° C. of the lubricant base oil is 25 mm²/s or less, excellent low-temperature viscosity properties can be obtained, and further satisfactory fuel efficiency can be obtained. When the dynamic viscosity at 40° C. of the lubricant base oil is 14 mm²/s or more, the oil film formation at the lubricating site is satisfactory so that excellent lubricating properties can be obtained, and further an evaporation loss of the lubricating oil composition can be suppressed.

Further, the lubricant base oil in the invention preferably has a viscosity index of 120 or more, further preferably 125 or more, more preferably 130 or more, especially preferably 132 or more. When the viscosity index of the lubricant base oil is 120 or more, there can be obtained a lubricating oil composition which can achieve excellent viscosity properties at temperatures in the range of from a low temperature to a high temperature, and which is unlikely to evaporate even when having a low viscosity. With respect to the upper limit of the viscosity index of the lubricant base oil, there is no particular limitation, and there can be used base oils having a viscosity index of about 125 to 180, such as a normal paraffin, a slack wax, and a GTL wax and isoparaffin mineral oils obtained by isomerizing the above paraffins, and base oils having a viscosity index of about 150 to 250, such as a complex ester base oil and an HVI-PAO base oil. With respect to the normal paraffin, slack wax, and GTL wax and isoparaffin mineral oils obtained by isomerizing the above paraffins, for improving the low-temperature viscosity properties, the viscosity index is preferably 180 or less, more preferably 170 or less, further preferably 160 or less, especially preferably 155 or less. In the invention, the viscosity index means a viscosity index as measured in accordance with JIS K2283-1993.

The lubricant base oil in the present embodiment preferably has a pour point of −10° C. or lower, more preferably −12.5° C. or lower, further preferably −15° C. or lower, especially preferably −17° C. or lower. When the pour point of the lubricant base oil is −10° C. or lower, the whole of the lubricating oil using the lubricant base oil tends to be improved in the low-temperature fluidity. The pour point in the invention means a pour point as measured in accordance with JIS K 2269-1987.

With respect to the lubricant base oil in the invention, as long as the above-mentioned requirements for the lubricant base oil are satisfied, a mineral oil-based base oil or a synthetic base oil can be individually used, or a mixture of two or more mineral oil-based base oils or two or more synthetic base oils may be used, or a mixture of a mineral oil-based base oil and a synthetic base oil may be used. The ratio of the two or more base oils in the mixture can be arbitrarily selected.

Examples of mineral oil-based base oils include paraffin and naphthene lubricant base oils, such as those which are obtained by refining a lubricating oil fraction, which is obtained by subjecting a crude oil to atmospheric distillation and vacuum distillation, using an appropriate combination of refining treatments, such as solvent deasphalting, solvent extraction, hydrocracking, solvent dewaxing, catalytic dewaxing, hydrorefining, cleaning with sulfuric acid, and a clay treatment.

Examples of synthetic base oils include poly-α-olefins (e.g., polybutene, a 1-octene oligomer, a 1-decene oligomer, and an ethylene-propylene oligomer) and hydrides thereof, isobutene oligomers and hydrides thereof, isoparaffins, alkylbenzenes, alkylnaphthalenes, diesters (e.g., dibutyl maleate, ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, and di-2-ethylhexyl sebacate), copolymers of an α-olefin and a diester, polyol esters (e.g., trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol-2-ethyl hexanoate, and pentaerythritol pelargonate), dialkyl diphenyl ethers, and polyphenyl ethers.

When the lubricant base oil in the invention is a mineral oil-based base oil, preferred is abase oil having a saturated hydrocarbon content of 90% or more. In the invention, the saturated hydrocarbon content means a value as measured in accordance with ASTM D-2007.

With respect to the base oil, preferred are those which are classified into the Group III or higher based on the classification of base oil according to the API (American Petroleum Institute) and base oils obtained by isomerizing waxes.

With respect to the method for producing the base oil, there is no particular limitation, but preferred is abase oil obtained by subjecting an atmospheric residual oil, which is obtained by subjecting a crude oil to atmospheric distillation, to desulfurization and hydrocracking and subjecting the resultant oil to fractional distillation into the set viscosity grade, or by subjecting the residual oil to solvent dewaxing or catalytic dewaxing and, if necessary, further to solvent extraction and hydrogenation. Especially, a base oil obtained by catalytic dewaxing is preferred.

In recent years, the lubricant base oil includes a petroleum wax-isomerized lubricant base oil which is obtained by hydro-isomerizing a petroleum wax by-produced in the dewaxing step in a base oil production process in which the atmospheric distillation residual oil is further subjected to vacuum distillation and fractional distillation into the required viscosity grade, and then subjected to a process, such as solvent refining or hydrorefining, followed by solvent dewaxing, and a GTL wax-isomerized lubricant base oil which is produced by a method of isomerizing a GTL WAX (gas-to-liquids wax) produced by a Fischer-Tropsch process or the like, and the like. A basic process for producing the wax-isomerized lubricant base oil is the same as the method for producing a hydrocracked base oil.

The % C_(p) of the base oil is not particularly limited, but is preferably 80 or more, more preferably 82 or more, further preferably 85 or more, especially preferably 86 or more, and is preferably 98 or less, further preferably 95 or less, especially preferably 90 or less, most preferably 88 or less. When the % C_(P) of the lubricant base oil is 80 or more, the viscosity-temperature characteristics, heat and oxidative stability, and frictional properties are likely to be improved, and further, when an additive is incorporated into the lubricant base oil, the effect of the additive is likely to be improved. Further, when the % C_(P) of the lubricant base oil is 98 or less, the solubility of an additive in the oil is likely to be improved.

The % C_(N) of the base oil is not particularly limited, but is preferably 20 or less, more preferably 15 or less, further preferably 14 or less, and is preferably 3 or more, more preferably 8 or more, especially preferably 10 or more. When the % C_(N) of the lubricant base oil is 20 or less, the viscosity-temperature characteristics, heat and oxidative stability, and frictional properties are likely to be improved. Further, when the % C_(N) of the lubricant base oil is 3 or more, the solubility of an additive in the oil is likely to be improved.

The % C_(A) of the base oil is not particularly limited, but is preferably less than 3, more preferably 2 or less, further preferably 1 or less, most preferably substantially 0. When the % C_(A) of the base oil is more than 10, the improvement of the heat resistance which is one of the objects of the invention is unsatisfactory.

The % C_(A) means a value as measured in accordance with the method described in ASTM D3238-85 (n-d-M ring analysis)

The saturated moiety content of the base oil is preferably 80 or more, more preferably 90 or more, further preferably 95 or more, especially preferably 98 or more, most preferably 99 or more. When the saturated moiety content of the base oil is 80 or more, the viscosity-temperature characteristics, heat and oxidative stability, and frictional properties are likely to be improved, and further, when an additive is incorporated into the lubricant base oil, the effect of the additive is likely to be improved.

The sulfur content of the base oil is not particularly limited, but is preferably 0.03% by mass or less, more preferably 0.01% by mass or less, and the base oil especially preferably contains substantially no sulfur. The smaller sulfur content means a higher degree of refining of the oil, which indicates that a problem of the solubility of sludge is unlikely to occur.

With respect to the method for measuring the sulfur content, there is no particular limitation, but JIS K2541-1996 or the like is generally used.

With respect to the evaporation loss of the base oil, there is no particular limitation. However, the evaporation loss of the base oil, in terms of a NOACK evaporation amount, is preferably 25% by mass or less, more preferably 21% by mass or less, further preferably 18% by mass or less, further preferably 16% by mass or less, especially preferably 15% by mass or less, most preferably 14% by mass or less. When the NOACK evaporation amount of the lubricant base oil is 25% by mass or less, the lubricating oil suffers less evaporation loss, and the cause of an increase of the viscosity or the like can be advantageously removed. The NOACK evaporation amount in the invention means an evaporation amount of a lubricating oil as measured in accordance with ASTM D 5800.

(B) Molybdenum-Based Friction Modifier

Examples of molybdenum-based friction modifiers in the invention include organomolybdenum-based friction modifiers containing sulfur, such as molybdenum dithiocarbamate (MoDTC) and molybdenum dithiophosphate (MoDTP). As specific examples of molybdenum dithiocarbamates, there can be mentioned compounds represented by the general formula (1) below. As specific examples of molybdenum dithiophosphates, there can be mentioned compounds represented by the general formula (2) below.

In the general formulae (1) and (2), each of R¹ to R⁸ independently represents a hydrocarbon group having 1 to 24 carbon atoms, and each of a, b, c, and d independently represents an integer of 0 to 4, wherein the relationships: a+b=4 and c+d=4 are satisfied.

As preferred examples of the hydrocarbon groups having 1 to 24 carbon atoms and being represented by R¹ to R⁸ in the general formulae (1) and (2), there can be individually mentioned linear or branched alkyl groups having 1 to 24 carbon atoms, cycloalkyl groups or linear or branched alkylcycloalkyl groups having 5 to 13 carbon atoms, linear or branched alkenyl groups having 3 to 24 carbon atoms, aryl groups or linear or branched alkylaryl groups having 6 to 18 carbon atoms, and arylalkyl groups having 7 to 19 carbon atoms. The alkyl group and alkenyl group may be primary, secondary, or tertiary.

With respect to the molybdenum-based friction modifier in the lubricating oil composition of the invention, in addition to those mentioned above, preferred examples include organomolybdenum complexes which are a reaction product of a basic nitrogen compound, such as succinimide, an acid molybdenum compound, such as molybdenum trioxide, and a sulfur compound, such as hydrogen sulfide or phosphorus pentasulfide.

In the lubricating oil composition of the invention, the amount of the molybdenum-based friction modifier contained, in terms of a molybdenum element content, based on the mass of the composition, is 0.005% by mass or more, more preferably 0.01% by mass or more, further preferably 0.03% by mass or more, especially preferably 0.05% by mass or more, and is 0.2% by mass or less, preferably 0.1% by mass or less. When the amount of the molybdenum-based friction modifier contained, in terms of a molybdenum element content, is less than 0.005% by mass, a remarkable fuel efficiency effect cannot be obtained. On the other hand, when the amount of the molybdenum-based friction modifier contained, in terms of a molybdenum element content, is more than 0 2% by mass, an. improvement of the fuel efficiency effect comparable to such a large amount of the friction modifier disadvantageously cannot be obtained.

In the lubricating oil composition of the invention, with respect to the molybdenum-based friction modifier, organomolybdenum-based friction modifiers containing sulfur are preferably used. Of these, molybdenum dithiophosphate or molybdenum dithiocarbamate is preferably used, and molybdenum dithiocarbamate is especially preferred because a synergy between molybdenum dithiocarbamate and the other component makes it possible to remarkably improve the fuel efficiency performance at temperatures in the range of from a low temperature to a high temperature.

(C) Salicylate-Based Metal Detergent

With respect to the salicylate-based metal detergent in the invention, an arbitrary compound generally used in a lubricating oil can be used. For example, an overbased compound of oil-soluble metal salt having a linear or branched hydrocarbon group and further having an OH group and/or a carbonyl group can be used. Further, there can be used an overbased metal salt of an alkaline earth metal salicylate, and an overbased metal salt obtained by reacting an alkaline earth metal hydroxide or oxide and, if necessary, boric acid or boric anhydride. The salicylate-based metal detergent is especially preferably a salicylate-based metal detergent containing boron. Examples of alkaline earth metals include magnesium, calcium, and barium, and calcium is preferred. With respect to the overbased metal salt, an oil-soluble metal salt of a compound containing an OH group and/or a carbonyl group overbased with an alkaline earth metal borate or alkaline earth metal carbonate is more preferably used. Particularly, from the viewpoint of excellent fuel efficiency, an alkaline earth metal salicylate is preferably used, and, an alkaline earth metal salicylate overbased with an alkaline earth metal borate is more preferably used.

The salicylate-based metal detergent in the invention preferably has a base number of 50 mg KOH/g or more, more preferably 100 mg KOH/g or more, further preferably 120 mg KOH/g or more, especially preferably 140 mg KOH/g or more, and preferably 300 mg KOH/g or less, more preferably 200 mg KOH/g or less. When the base number of the salicylate-based metal detergent is less than 50 mg KOH/g, it is likely that the viscosity is markedly increased to cause the fuel efficiency to be poor and further the friction reducing effect obtained by the addition of the salicylate-based metal detergent is unsatisfactory. Further, when the base number of the salicylate-based metal detergent is more than 300 mg KOH/g, it is likely that the effect of a wear resistant additive or the like is inhibited and the friction reducing effect is unsatisfactory. The base number in the invention is a value as measured in accordance with JIS K 2501 5.2.3.

The method for producing the salicylate-based metal detergent used in the invention is arbitrary, but, for example, the salicylate-based metal detergent is obtained by reacting the above-mentioned oil-soluble metal salt, an alkaline earth metal hydroxide or oxide, and, if necessary, boric acid or boric anhydride in the presence of water, an alcohol, such as methanol, ethanol, propanol, or butanol, and a diluent solvent, such as benzene, toluene, or xylene, at 20 to 200° C. for 2 to 8 hours, and then heating the resultant reaction mixture to 100 to 200° C. to remove water and, if necessary, the alcohol and diluent solvent. The detailed reaction conditions are appropriately selected according to the amounts of the raw materials and reactants. The details of the method for producing the salicylate-based metal detergent are described in, for example, JP-A-60-116688, JP-A-61-204298 and the like. The total base number of the oil-soluble metal salt overbased with an alkaline earth metal borate produced by the above-mentioned method is generally 100 mg KOH/g or more, and therefore the oil-soluble metal salt can be preferably used in the lubricating oil composition of the invention.

The salicylate-based metal detergent in the invention preferably has a metal ratio of 4.0 or less, more preferably 3.0 or less, further preferably 2.0 or less. When the metal ratio of the salicylate-based metal detergent is more than 4.0, the reduction of the frictional torque, that is, the fuel efficiency can be unsatisfactory. Further, the metal detergent has a metal ratio adjusted to preferably 1.0 or more, more preferably 1.1 or more, further preferably 1.5 or more. When the metal ratio of the salicylate-based metal detergent is less than 1.0, the resultant lubricating oil composition for internal combustion engine is increased in dynamic viscosity or low-temperature viscosity, so that a problem can be caused in the fuel efficiency or starting properties.

The metal ratio in the invention is represented by: Valence of the metal element in the metal detergent×Metal element content (mol %)/Soap group content (mol %), wherein the metal element means calcium, magnesium, or the like, and the soap group means a sulfonic acid group, a phenol group, salicylic acid group, or the like.

The linear or branched hydrocarbon group in the salicylate-based metal detergent in the invention is preferably an alkyl group or alkenyl group, and the alkyl group or alkenyl group preferably has 8 or more carbon atoms, more preferably 10 or more carbon atoms, further preferably 12 or more carbon atoms, and preferably has 19 carbon atoms or less. The alkyl group or alkenyl group having less than 8 carbon atoms disadvantageously causes the oil solubility to be unsatisfactory. The alkyl group or alkenyl group may be either linear or branched, but is preferably linear, and may be a primary alkyl group or alkenyl group, a secondary alkyl group or alkenyl group, or a tertiary alkyl group or alkenyl group, but, when these are a secondary alkyl group or alkenyl group or a tertiary alkyl group or alkenyl group, preferred are those in which branching is positioned only at the carbon bonded to the aromatic ring.

The amount of the contained salicylate-based metal detergent in the invention, in terms of a metal element content, based on the mass of the lubricating oil composition, is 0.01% by mass or more, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, especially preferably 0.15% by mass or more, and is 1% by mass or less, preferably 0.5% by mass or less, more preferably 0.4% by mass or less, further preferably 0.3% by mass or less, especially preferably 0.25% by mass or less, most preferably 0.2% by mass or less. When the amount of the salicylate-based metal detergent contained is less than 0.01% by mass, it is likely that the friction reducing effect obtained by the addition of the salicylate-based metal detergent is unsatisfactory, and the resultant lubricating oil composition is unsatisfactory in the fuel efficiency, heat and oxidative stability, and cleanability. On the other hand, when the amount of the salicylate-based metal detergent contained is more than 1% by mass, it is likely that the friction reducing effect obtained by the addition of the salicylate-based metal detergent is unsatisfactory, and the resultant lubricating oil composition is unsatisfactory in the fuel efficiency.

When a salicylate-based metal detergent containing boron is used as the salicylate-based metal detergent, the amount of boron contained in the lubricating oil composition, in terms of a boron element content, based on the mass of the lubricating oil composition, is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, further preferably 0.03% by mass or more, especially preferably 0.04% by mass or more, and is preferably 0.2% by mass or less, more preferably 0.1% by mass or less, further preferably 0.09% by mass or less, especially preferably 0.08% by mass less. When the amount of boron contained is 0.001% by mass or more, it is likely that the friction reducing effect obtained by the addition of the salicylate-based metal detergent is satisfactory, and the resultant lubricating oil composition is satisfactory in the fuel efficiency, heat and oxidative stability, and cleanability. On the other hand, when the amount of boron contained is 0.2% by mass or less, it is likely that the friction reducing effect obtained by the addition of the salicylate-based metal detergent is satisfactory, and the resultant lubricating oil composition is satisfactory in the fuel efficiency.

(D) Ash-Free Friction Modifier

In the invention, as an ash-free friction modifier, at least one of amino acids having an alkyl group, alkenyl group, or acyl group having 15 to 24 carbon atoms and/or derivatives thereof is contained. As examples of such compounds, there can be mentioned compounds represented by the following general formula (3).

In the above formula, R⁹ is an alkyl group, alkenyl group, or acyl group having 15 to 24 carbon atoms, R¹⁰ is an alkyl group having 1 to 4 carbon atoms or hydrogen, and R¹¹ is hydrogen or an alkyl group having 1 to 10 carbon atoms. The alkyl group may contain a linear, branched, or cyclic structure, and fray have a carbon atom replaced by a heteroatom, and may be modified with a functional group, such as a hydroxyl group, a carboxyl group, or an amino group. R¹² is an alkyl group having 1 to 4 carbon atoms or hydrogen, n is 0 or 1, and X is a functional group having active hydrogen, a hydrocarbon having the functional group, a metal salt or ethanolamine salt of the functional group, or a methoxy group.

From the viewpoint of the solubility in the base oil, low frictional properties, fuel efficiency, and the like, R⁹ in the general, formula (3) is more preferably an alkyl group, alkenyl group, or acyl group having 16 or more carbon atoms, further preferably an alkyl group, alkenyl group, or acyl group having 17 or more carbon atoms, especially preferably an alkyl group, alkenyl group, or acyl group having 18 or more carbon atoms. Further, from the viewpoint of the storage stability, the alkyl group, alkenyl group, or acyl group preferably has 23 carbon atoms or less, further preferably 20 carbon atoms or less, especially preferably 19 carbon atoms or less, most preferably 18 carbon atoms. Further, from the viewpoint of the friction reducing effect, the alkyl group, alkenyl group, or acyl group is preferably linear. Specific examples of such alkyl groups, alkenyl groups, and acyl groups include alkyl groups, such as a pentadecyl group, a hexadecyl group, heptadecyl group, an octadecyl group, a nonadecyl group, an icosyl group, a heneicosyl group, a docosyl group, a tricosyl group, and a tetracosyl group (wherein the alkyl groups may be linear or branched), alkenyl groups, such as a pentadecenyl group, a hexadecenyl group, a heptadecenyl group, an octadecenyl group, a nonadecenyl group, an icosenyl group, a heneicosenyl group, a docosenyl group, a tricosenyl group, and a tetracosenyl group (wherein the alkenyl groups may be linear or branched, and have a double bond at an arbitrary position), and acyl groups having a ketone group at, the end of the above alkyl group or alkenyl group.

From the viewpoint of the storage stability and the like, R¹⁰ in the general formula (3) is more preferably an alkyl group having 4 carbon atoms or less, further preferably an alkyl group having 3 carbon atoms or less, especially preferably an alkyl group having 2 carbon atoms or less.

The alkyl group for R¹¹ may contain a linear, branched, or cyclic structure, and may have a carbon atom replaced by a heteroatom, and may be modified with a functional group, such as a hydroxyl group, a carboxyl group, or an amino group. From the viewpoint of the friction reducing effect, the solubility in the base oil, and the like, R¹¹ is more preferably an alkyl group having 2 carbon atoms or less, further preferably an alkyl group having carbon atom or less, especially preferably hydrogen.

From the viewpoint of the storage stability and the like, R12 is more preferably an alkyl group having 4 carbon atoms or less, further preferably an alkyl group having 3 carbon atoms or less, especially preferably an, alkyl group having 2 carbon atoms or less, most preferably hydrogen.

The functional group having active hydrogen for X in the general formula (3) is preferably a hydroxyl group, an amino group, or the like. The amino group is preferably a primary or secondary amine, especially preferably a primary amine. As examples of metal salts of the active hydrogen group, there can be mentioned metal salts of a hydroxyl group. Of these, —COX in the general formula (3) is preferably a carboxyl group.

Specific examples of hydrocarbons having a hydroxyl group, which are functional groups having active hydrogen, include dihydric alcohols, such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,2-butanediol, neopentyl glycol, 1,6-hexanediol, 1,2-octanediol, 1,8-octanediol, isoprene glycol, 3-methyl-1,5-pentanediol, sorbite, catechol, resorcin, hydroquinone, bisphenol A, bisphenol F, hydrogenated bisphenol. A, hydrogenated bisphenol F, and dimer diol; trihydric alcohols, such as glycerol, 2-(hydroxymethyl)-1,3-propanediol, 1,2,3-butanetriol, 1,2,3-pentanetriol, 2-methyl-1,2,3-propanetriol, 2-methyl-2,3,4-butanetriol, 2-ethyl-1,2,3-butanetriol, 2,3,4-pentanetriol, 2,3,4-hexanetriol, 4-propyl-3,4,5-heptanetriol, 2,4-dimethyl-2,3,4-pentanetriol, 1,2,4-butanetriol, 1,2,4-pentanetriol, trimethylolethane, and trimethylolpropane; tetrahydric alcohols, such as pentaerythritol, erythritol, 1,2,3,4-pentanetetrol, 2,3,4,5-hexanetetrol, 1,2,4,5-pentanetetrol, 1,3,4,5-hexanetetrol, diglycerol, and sorbitan; pentahydric alcohols, such as adonitol, arabitol, xylitol, and triglycerol; hexahydric alcohols, such as dipentaerythritol, sorbitol, mannitol, iditol, inositol, dulcitol, talose, and allose; and polyglycerol and condensation products thereof.

Examples of metals in the hydroxyl group metal salt include alkali metals, alkaline earth metals, and zinc, and examples of alkali metals and alkaline earth metals include sodium, potassium, magnesium, and calcium. Of these, from the viewpoint of improving the persistence of the frictional property effect, alkaline earth metals and zinc are preferred.

Among the metal salts of the general formula (3), preferred are carboxylic acid salts of the general formula (3) in which —COX is a carboxyl group structure.

With respect to the ash-free friction modifier in the invention, from the viewpoint of improving the persistence of the frictional property effect and the like, preferred is at least one compound selected from the compounds of general formula (3), and only one type of compound selected from the compounds of general formula (3) may be individually used, or two or more types of the compounds may be used in the form of a mixture.

As preferred examples of the compounds represented by the general formula (3), there can be mentioned N-acylsarcosine, especially N-oleoylsarcosine which is a compound of the formula (3) wherein R⁹ is an acyl group having 18 carbon atoms, R¹⁰ is a methyl group, R¹¹ is hydrogen, X is a hydroxyl group, and n is 0, and N-oleoyl-N-methyl-β-alanine which is a compound of the formula (3) wherein R⁹ is an acyl group having 18 carbon atoms, R¹⁰ is a methyl group, R¹¹ is hydrogen, R¹² is hydrogen, X is a hydroxyl group, and n is 1.

The amount of the ash-free friction modifier contained is 0.01 to 10% by mass, preferably 5% by mass or less, more preferably 2% by mass or less, based on the mass of the composition. When the amount of the ash-free friction modifier contained is more than 10% by mass, a further improvement of the frictional properties comparable to such a large amount of the friction modifier cannot be obtained, and the storage stability disadvantageously becomes poor. On the other hand, the amount of the ash-free friction modifier contained is preferably 0.05% by mass or More, more preferably 0.1% by mass or less, based on the mass of the composition. When the amount of the ash-free friction modifier contained is less than 0.01% by mass, the improvement effect for the frictional properties is disadvantageously not obtained.

(E) Anti-Wear Agent

In the lubricating oil composition for internal combustion engine of the invention, in addition to the above-mentioned additive, zinc dialkyldithiophosphate (ZnDTP) is preferably further added as an anti-wear agent. As examples of such compounds, there can be mentioned compounds represented by the following general formula (4).

In the general formula (4) above, each of R¹³ to R¹⁶ is independently hydrogen or at least one of them is a linear or branched alkyl group having 1 to 24 carbon atoms, and the alkyl group may be primary, secondary, or tertiary.

In the invention, these zinc dialkyldithiophosphates may be used individually or in combination, but preferred is zinc dithiophosphate having a primary alkyl group (primary ZnDTP) or zinc dithiophosphate having a secondary alkyl group (secondary ZnDTP), and especially preferred is one which is mainly made of zinc dithiophosphate having a secondary alkyl group because the wear resistance is improved.

In the lubricating oil composition of the invention, the zinc dialkyldithiophosphate is incorporated so that the amount of the zinc dialkyldithiophosphate contained, in terms of a phosphorus content, based on the mass of the composition, is preferably 0.02 to 0.2% by mass, more preferably 0.03 to 0.1% by mass. When the phosphorus content is less than 0.02% by mass, the wear resistance and high-temperature cleanability are not satisfactory. When the phosphorus content is more than 0.2% by mass, an exhaust gas catalyst disadvantageously suffers severe catalytic poison.

In the lubricating oil composition for internal combustion engine of the invention, if necessary, other additives, for example, a viscosity index improver, a pour point depressant, an antioxidant, a wear resistant agent or an extreme-pressure agent, a friction reducing agent, a dispersant, a rust preventive agent, a surfactant or a demulsifier, an anti-foaming agent, or the like can be appropriately incorporated in such an amount that the object of the invention is riot sacrificed.

For example, as a viscosity index improver, a non-dispersion-type viscosity index improver or a dispersion-type viscosity index improver can be used. Specifically, a non-dispersion-type or dispersion-type polymethacrylate or olefin copolymer, or polyisobutene, polystyrene, an ethylene-propylene copolymer, a styrene-diene copolymer, a hydride thereof, or the like can be used. The weight average molecular weight of the above viscosity index improver is generally 5,000 to 1,000,000, but, for further improving the fuel efficiency performance, the viscosity index improver having a weight average molecular weight of 100,000 to 1,000,000, preferably 200,000 to 900,000, especially preferably 400,000 to 800,000 is desirably used. In the invention, for improving the fuel efficiency, particularly, the viscosity index improver is preferably a poly(meth)acrylate viscosity index improver in which the amount of the structural units represented by the general formula (5) below is 30 to 90 mol %, the amount of the structural units represented by the general formula (6) below is 0.1 to 50 mol %, and the hydrocarbon principal chain ratio is 0.18 or less.

In the general formula (5) above, R¹⁷ represents hydrogen or a methyl group, and R¹⁸ represents a linear or branched hydrocarbon group having 6 carbon atoms or less. In the general formula (6), R¹⁹ represents hydrogen or a methyl group, and R²⁰ represents a linear or branched hydrocarbon group having 16 or more carbon atoms.

The viscosity index improver preferably has a PSSI (permanent shear stability index) in a diesel injector method of 30 or less. When the PSSI of the viscosity index improver is more than 30, the shear stability is poor, and the dynamic viscosity or HTHS viscosity after being used is maintained at a constant value or more, and hence the initial fuel efficiency may become poor.

The expression “PSSI in a diesel injector method” means a permanent shear stability index of a polymer calculated based on the data measured by ASTM D6278-02 (Test Method for Shear Stability of Polymer Containing Fluids Using a European Diesel. Injector Apparatus) in accordance with ASTM D6022-01 (Standard Practice for Calculation of Permanent Shear Stability Index).

As pour point depressant, for example, a polymethacrylate polymer which can be applied to the lubricant base oil used, an alkylated aromatic compound, a fumarate-vinyl acetate copolymer, an ethylene-vinyl acetate copolymer, or the like can be used.

As a dispersant, succinimide, benzylamine, alkylpolyamine, polybuteneamine, or a modification product thereof with a boron compound or a sulfur compound, an alkenylsuccinate, or the like can be used.

The dispersant is preferably a mono-type or bis-type succinimide, more preferably a bis-type succinimide. Further, a bis-type succinimide containing no boron is especially preferred.

Further, the dispersant preferably has a molecular weight of 1,000 or more, more preferably 5,000 or more, more preferably 7,000 or more, further preferably 9,000 or more. Further, the molecular weight of the cleaning dispersant is preferably 30,000 or less, preferably 25,000 or less, more preferably 20,000 or less. When the molecular weight of the dispersant is 1,000 or less, the cleanability may be unsatisfactory. On the other hand, when the molecular weight of the dispersant is more than 30,000, the resultant engine oil composition may become very poor in the fuel efficiency.

The amount of the dispersant contained is preferably 0.1. to 15% by mass, more preferably 0.5 to 10% by mass, further preferably 1.0 to 8% by mass, based on the mass of the engine oil composition. When the amount of the cleaning contained is less than 0.1% by mass, the cleanability may be unsatisfactory. On the other hand, when the amount of the dispersant contained is more than 15% by mass, the resultant engine oil composition may become very poor in the fuel efficiency.

The N content of the dispersant is preferably 0.1 or more, more preferably 0.3 or more, more preferably 0.4 or more, further preferably 0.5 or more, and is preferably 2.0 or less, preferably 1.0 or less, more preferably 0.8 or less. When the N content of the dispersant is 0.1 or less, the cleanability may be unsatisfactory. On the other hand, when the N content of the dispersant is more than 2.0, the resultant engine oil composition may become very poor in the fuel efficiency.

As an antioxidant, any antioxidant, such as a phenol compound or an amine compound, which is generally used in a lubricating oil, can be used. For example, an alkylphenol, such as 2,6-di-tert-butyl 4 methylphenol, a bisphenol, such as methylene-4,4-bis(2,6-di-tert-butyl-4-methylphenol), a naphthylamine, such as phenyl-α-naphthylamine, a dialkyldiphenylamine, a phenothiazine, or the like cart be used.

Examples of extreme-pressure additives and anti-wear agents include phosphorus compounds, such as phosphates, phosphites and salts thereof, and sulfur compounds, such as disulfides, olefin sulfides, and sulfurized oils and fats.

As a rust preventive agent, for example, an alkenylsuccinic acid, an alkenylsuccinate, a polyhydric alcohol ester, petroleum sulfonate, dinonyl naphthalenesulfonate, or the like can be used.

As a corrosion inhibitor, for example, a benzotriazole, thiadiazole, or imidazole compound can be used.

As an anti-foaming agent, for example, a silicone compound, such as dimethylsilicone or fluorosilicone, can be used.

The amount of the above additive added is arbitrary, but, generally, based on the mass of the composition, the amount of the anti-foaming agent contained is 0.0005 to 0.01% by mass, the amount of the viscosity index improver contained is 0.05 to 20% by mass, the amount of the corrosion inhibitor contained is 0.005 to 0.2% by mass, and the amount of each of the other additives contained is about 0.05 to 10% by mass.

The lubricating oil composition for internal combustion engine of the invention preferably has a dynamic viscosity at 100° C. of 4.0 mm²/s or more, more preferably 6.0 mm²/s or more, further preferably 6.1 mm²/s or more, most preferably 6.2 mm²/s or more, and preferably 12.5 mm²/s or less, more preferably 9.3 mm²/s or lees, further preferably 8.5 mm²/s or less. The dynamic viscosity at 100° C. in the invention indicates a dynamic viscosity at 100° C. defined in ASTM D-445. When the dynamic viscosity at 100° C. of the lubricating oil composition is less than 4.0 mm²/s, the lubricating properties may be unsatisfactory. When the dynamic viscosity at 100° C. of the lubricating oil composition is more than 12.5 mm²/s, there is a danger that the required low-temperature viscosity and satisfactory fuel efficiency performance cannot be obtained.

The dynamic viscosity at 40° C. of the lubricating oil composition is preferably 4 to 50 mm²/s, preferably 40 mm²/s or less, more preferably 35 mm²/s or less. Further, the dynamic viscosity at 40° C. of the lubricating oil composition is preferably 15 mm²/s or more, more preferably 18 mm²/s or more, further preferably 20 mm²/s or more, especially preferably 22 mm²/s or more, most preferably 25 mm²/s or more. The dynamic viscosity at 40° C. in the invention indicates a dynamic viscosity at 40° C. defined in ASTM D-445. When the dynamic viscosity at 40° C. of the lubricating oil composition is less than 4 mm²/s, the lubricating properties may be unsatisfactory. When the dynamic viscosity at 40° C. of the lubricating oil composition is more than 50 mm²/s, there is a danger that the required low-temperature viscosity and satisfactory fuel efficiency performance cannot be obtained.

Further, the viscosity index of the lubricating oil composition is preferably 120 to 400, and is preferably 190 or more, further preferably 200 or more, especially preferably 210 or more. When the viscosity index of the lubricating oil composition is less than 120, it may be difficult to improve the fuel efficiency while maintaining the HTHS viscosity at 150° C. Further, when the viscosity index of the lubricating oil composition is more than 400, there is a danger that the evaporation properties become poor and further a problem is caused due to a lack of the solubility of an additive or the application property to a sealing material.

For imparting fuel efficiency to a lubricating oil while preventing a problem of reduction of the viscosity and maintaining the durability, increasing the HTHS viscosity at 150° C. (“HTHS viscosity” is referred to also as “high-temperature high-shear viscosity”) and reducing the dynamic viscosity at 40° C., the dynamic viscosity at 100° C., and the HTHS viscosity at 100° C. are effective. However, in a conventional lubricating oil, it has been very difficult to meet all the requirements.

The lubricating oil composition preferably has an HTHS viscosity at 100° C. of 5.5 mPa·s or less, more preferably 5.0 mPa·s or less, further preferably 4.7 mPa·s or less, especially preferably 4.5 mPa·s or less, and preferably 3.0 mPa·s or more, further preferably 3.5 mPa·s or more, especially preferably 4.0 mPa·s or more, most preferably 4.1 mPa·s or more. The HTHS viscosity at 100° C. in the invention indicates high-temperature high-shear viscosity at 100° C. defined in ASTM D4683. When the HTHS viscosity at 100° C. of the lubricating oil composition is less than 3.0 mPa·s, the lubricating properties may be unsatisfactory. When the HTHS viscosity at 100° C. of the lubricating oil composition is more than 5.5 mPa·s, there is a danger that the required low-temperature viscosity and satisfactory fuel efficiency performance cannot be obtained.

The lubricating oil composition preferably has an HTHS viscosity at 150° C. of 1.5 mPa·s or more, more preferably 1.9 mPa·s or more, further preferably 2.1 mPa·s or more, especially preferably 2.2 mPa·s or more, most preferably 2.3 mPa·s or more, and preferably 3.0 mPa·s or less, further preferably 2.7 mPa·s or less, especially preferably 2.5 mPa·s or less, most preferably 2.4 mPa·s or less. The HTHS viscosity at 150° C. in the invention indicates a high-temperature high-shear viscosity at. 150° C. defined in ASTM D4683. When the HTHS viscosity at 150° C. of the lubricating oil composition is 1.5 mPa·s or more, satisfactory lubricating properties can be obtained. When the HTHS viscosity at 150° C. of the lubricating oil composition is 3.0 mPa·s or less, the required low-temperature viscosity and satisfactory fuel efficiency performance are obtained.

The ratio of the HTHS viscosity at 150° C. to the HTHS viscosity at 100° C. of the lubricating oil composition of the invention (HTHS viscosity at 150° C./HTHS viscosity at 100° C.) is preferably 0.45 or more, more preferably 0.475 or more, further preferably 0.50 or more. When the ratio is less than 0.45, there is a danger that the required low-temperature viscosity and satisfactory fuel efficiency performance cannot be obtained.

Further, the lubricating oil composition of the invention preferably has an evaporation loss, in terms of a NOACK evaporation amount, of 15% by mass or less, more preferably 14% by mass or less, further preferably 13% by mass or less, most preferably 12% by mass or less. When the NOACK evaporation amount of the lubricant base oil component is 15% by mass or less, an evaporation loss of the lubricating oil can be reduced, and an increase of the viscosity and the like can be suppressed. The NOACK evaporation amount in the invention indicates an evaporation amount of a lubricating oil as measured in accordance with ASTM D 5800.

When an alkaline earth metal salicylate detergent containing boron is used as the salicylate-based metal detergent, the ratio of the amount of boron contained (MB1) to the amount of the alkaline earth metal contained (MB2) in the lubricating oil composition of the invention, i.e., the (MB1)/(MB2) ratio is preferably 0.1 or more, more preferably 0.15 or more, further preferably 0.2 or more. Further, the (MB1)/(MB2) ratio is preferably 0.5 or less, more preferably 0.4 or less, further preferably 0.3 or less.

EXAMPLES

Hereinbelow, the present invention will be described in more detail with reference to the following Examples and Comparative Examples, which should not be construed as limiting the scope of the invention.

Examples 1 to 4 and Comparative Examples 1 to 4 (A) Lubricant Base Oil

A hydrocracked lubricant base oil having the properties shown in Table 1 was used and incorporated in the formulation shown in Table 2.

TABLE 1 Properties unit value Density (15° C.) g/cm³ 0.820 Dynamic viscosity mm²/s 17.8 (40° C.) Dynamic viscosity mm²/s 4.07 (100° C.) Viscosity index 132 Pour point ° C. −22.5 NOACK mass % 13.4 Sulfur content mass ppm <1 Nitrogen content mass ppm <3 n-d-M Analysis % CP 87.3 % CN 12.7 % CA 0 Chromatographic mass % 99.6 (Saturated moiety content) fractionation 0.2 (Aromatic content) 0.2 (Resin content) Recovery rate % 100

Additives shown below were added to the lubricant base oil in the formulation shown in Table 2 to prepare a lubricating oil composition.

(B) Molybdenum-Based Friction Modifier

-   Molybdenum dithiocarbamate: In the general formula (I), R¹ to R⁴ are     an alkyl group having 8 or 13 carbon atoms, a and b are 2, the     molybdenum element concentration is 10% by mass, and the sulfur     content is 11% by mass.

(C) Salicylate-Based Metal Detergent

-   (C-1) Overbased Ca salicylate: metal ratio: 2.3; number of carbon     atoms of the alkyl group: 14 to 18; Ca content: 6.2% by mass; base     number: 180 mg KOH/g -   (C-2) Overbased Ca salicylate borate: metal ratio: 2.5; number of     carbon atoms of the alkyl group: 14 to 18; Ca content: 6.8% by mass;     B content: 2.7% by mass; base number: 190 mg KOH/g

(D) Ash-Free Friction Modifier

-   (D-1) N-Oleoyl-N-methyl-β-alanine -   (D-2) Oleoylsarcosine -   (D-3) N-Lauroyl-N-methyl-β-alanine -   (D-4) N-Lauroylsarcosine

(E) Anti-Wear Agent

-   (E-1) ZnDTP: number of carbon atoms of the primary alkyl group: 8;     Zn content: 9.0% by mass; P content: 7.4% by mass; S content: 15% by     mass -   (E-2) ZnDTP: number of carbon atoms of the secondary alkyl group: 4     and 6; Zn content: 8.0% by mass; P content: 7.2% by mass; S content:     15% by mass

(F) Other Additives

-   (F-1) Non-dispersion-type PMA viscosity index improver (Mw=400,000,     PSSI=7) -   (F-2) Polybutenylsuccinimide: molecular weight: 9,000; N content:     0.7% by mass -   (F-3) Antioxidant, anti-foaming agent (dimethylsilicone), arid the     like

With respect to the prepared lubricating oil composition, a motoring friction test was conduced under the conditions shown below to measure a frictional torque. An average frictional torque of each lubricating oil composition was calculated, and an improvement ratio relative to the frictional torque in Comparative Example 1 or 4 as a reference was calculated. The obtained results in terms of % as well as the physical properties of the lubricating oil compositions are shown in Table 2.

(Test conditions)

-   Engine used: 3 L, DOHC engine -   Oil temperature: 80° C. -   Number of revolutions: 550 rpm

TABLE 2 Com- Com- Com- Com- Example Example Example Example parative parative parative parative 1 2 3 4 Example 1 Example 2 Example 3 Example 4 Base oil (A) Balance Balance Balance Balance Balance Balance Balance Balance Additive (B) 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 (based on the (C-1) 3.0 3.0 1.5 3.0 3.0 3.0 3.0 3.0 mass of the (C-2) 1.5 composition, (D-1) 0.5 % by mass) (D-2) 0.5 0.5 0.5 (D-3) 0.4 (D-4) 0.4 (E-1) 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 (E-2) 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 (F-1 ) 5.3 5.3 5.3 7.7 5.3 5.3 5.3 5.3 (F-2) 3.2 3.2 3.2 3.2 3.2 3.2 3.2 3.2 (F-3) 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Dynamic  40° C mm²/s 26.4 26.5 26.5 28.7 26.4 26.5 36.4 28.7 viscosity 100° C. mm²/s 6.5 6.5 6.5 7.3 6.5 6.5 6.5 7.3 Viscosity Index 214 214 214 235 214 214 215 235 HTHS 100° C. mPa · s 4.5 4.5 4.5 4.8 4.5 4.5 4.5 4.8 Viscosity 150° C. mPa · s 2.3 2.3 2.3 2.6 2.3 2.3 2.3 2.6 NOACK 250° C., 1 h mass % 12 12 12 12 12 12 12 12 Element in oil B ppm 0.00 0.00 0.04 0.00 0.00 0.00 0.00 0.00 Ca ppm 0.20 0.20 0.20 0.20 0.20 0.20 0.20 0.20 Mortering test Torque Improve- % 2.8 3.0 3.5 — Reference 0.8 0.9 — ment ratio (relative to Comparative Example 1) Torque Improve- % — — — 2.1 — — — Reference ment ratio (relative to Comparative Example 4)

As can be seen from the above results, even when containing a molybdenum-based friction modifier and a compound selected from amino acids having in the molecule thereof an alkyl group, alkenyl group, or acyl group and/or derivatives thereof, the lubricating oil composition containing the compound having alkyl group, alkenyl group, or acyl group having less than 15 carbon atoms exhibits a poor effect (Comparative Examples 1 to 4), whereas the lubricating oil composition containing a compound selected from amino acids having an alkyl group, alkenyl group, or acyl group having 15 to 24 carbon atoms and/or derivatives thereof exhibits remarkable friction reduction effect. From the above, it is apparent that the lubricating oil composition for internal combustion engine of the invention exhibits remarkable effects such that it has a low coefficient of friction and excellent fuel efficiency performance.

INDUSTRIAL APPLICABILITY

The lubricating oil composition for internal combustion engine of the invention can be advantageously used as a fuel-efficient engine oil, such as a fuel-efficient gasoline engine oil or a fuel-efficient diesel engine oil. 

1. A lubricating oil composition for internal combustion engine, containing (A) a lubricant base oil having a dynamic viscosity of 2.0 to 5.0 mm²/s at 100° C., (B) a molybdenum-based friction modifier in an amount of 0.005 to 0.2% by mass, in terms of a molybdenum content, based on the mass of the composition, (C) a salicylate-based metal detergent in an amount of 0.01 to 1% by mass, in terms of a metal content, based on the mass of the composition, and (D) at least one compound selected from amino acids having an alkyl group, alkenyl group, or acyl group having 15 to 24 carbon atoms and/or derivatives thereof in an amount of 0.01 to 10% by mass.
 2. The lubricating oil composition for internal combustion engine according to claim 1, wherein the salicylate-based metal detergent (C) is a salicylate-based metal detergent containing boron.
 3. The lubricating oil composition for internal combustion engine according to claim 1, which has an HTHS viscosity of 1.9 to 2.7 mPa/s at 150° C.
 4. The lubricating oil composition for internal combustion engine according to claim 1, which has an HTHS viscosity of 1.9 to 2.4 mPa/s at 150° C.
 5. The lubricating oil composition for internal combustion engine according to claim 1, which has a NOACK evaporation amount of 15% by mass or less.
 6. The lubricating oil composition for internal combustion engine according to claim 1, which contains (E) a zinc dialkyldithiophosphate anti-wear agent in an amount of 0.02 to 0.20% by mass, in terms of a phosphorus content, based on the mass of the composition. 